1. Field of the Invention
The instant invention relates to a process for activating iridium-containing catalysts, said catalysts being inactive because of the presence of the iridium as large crystallites of low activity, and which comprises the step of contacting said catalyst with a halogen-containing gas and oxygen, the oxygen being present in an amount of less than 10% by volume oxygen, at an elevated temperature for a time sufficient to redisperse said large crystallites to crystallites having a substantially smaller particle size. Preferably, the catalyst is a reforming catalyst comprising iridium supported on alumina. In the most preferred embodiment of the instant invention an iridium or iridium:platinum on alumina catalyst, which has become deactivated by use in a reforming process wherein carbonaceous materials have deposited on the surface of the catalyst, is regenerated by (1) burning off at least a portion of said carbonaceous deposits by contacting said catalyst with oxygen at a temperature of at least 300.degree.C., (2) contacting said catalyst with hydrogen at a temperature and time sufficient to reduce at least a portion of the iridium to its metallic form, and (3) redispersing the iridium by contacting said reduced catalyst with a halogen-containing gas, e.g., chlorine and oxygen, the oxygen being present in an amount less than 10% oxygen by volume, but sufficient to enhance the redispersion of the iridium on the catalyst and at a temperature of at least 300.degree.C.
2. Description of the Prior Art
U.S. Pat. No. 3,134,732 teaches that noble metal hydrocarbon conversion catalysts may be reactivated, after burning off carbonaceous deposits, by contacting said catalysts with chlorine gas at a temperature of from 60.degree.F. (.about.15.degree.C) to 1250.degree.F. (.about.677.degree.C) for a time sufficient to restore said catalyst to initial activity. Mixtures of chlorine gases with inert gases or oxygen are taught to be equivalent to 100% chlorine so long as an amount of chlorine equal to from 0.1 to 10% by weight catalyst is contacted with said catalyst. Further inventions in this area include U.S. Pat. No. 3,020,240 which teaches the use of chlorine and an optimum of 20 mole % of oxygen in a process for reactivating catalysts, and U.S. Pat. No. 3,243,384 which teaches the use of steam, air and chlorine mixtures in regenerating or activating a platinum on alumina catalyst. All of the above patents are mainly interested in platinum as the catalyst metal and mention of other catalyst metals is merely incidental.
U.S. Pat. No. 3,147,229 discloses the importance of maintaining high metal surface areas in platinum, palladium or rhodium on alumina catalysts for hydrocarbon conversions. The high metal areas are achieved by regenerating the catalyst in the presence of a chlorine in air mixture to restore metal surface area (redispersion of the metal).